scsi: sd: Fix off-by-one error in sd_read_block_characteristics()

Ff the device returns page 0xb1 with length 8 (happens with qemu v2.x, for
example), sd_read_block_characteristics() may attempt an out-of-bounds
memory access when accessing the zoned field at offset 8.

Fixes: 7fb019c ("scsi: sd: Switch to using scsi_device VPD pages")
Cc: [email protected]
Signed-off-by: Martin Wilck <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Martin K. Petersen <[email protected]>

Author: mwilck

drivers/scsi/sd.c

@@ -3402,7 +3402,7 @@ static void sd_read_block_characteristics(struct scsi_disk *sdkp,
 	rcu_read_lock();
 	vpd = rcu_dereference(sdkp->device->vpd_pgb1);
 
-	if (!vpd || vpd->len < 8) {
+	if (!vpd || vpd->len <= 8) {
 		rcu_read_unlock();
 	        return;
 	}